Recently, as environmental problems have become an important issue, interest in methods of efficiently processing exhaust gas of the vehicle has increased. Nitrogen oxide (NOx) included in exhaust gas is considered as main air pollutants, and a number of researches are being conducted to reduce emission of NOx.
An exhaust gas recirculation (EGR) system mounted in a vehicle reduces noxious exhaust gases of the vehicle. Generally, the amount of NOx in the exhaust gas is increased in an oxygen rich air mixture, and the air mixture is combusted well. Therefore, the exhaust gas recirculation system reduces the amount of NOx in the exhaust gas as a consequence of a part (e.g., 5-20%) of the exhaust gas being recirculated to the air mixture in order to reduce the oxygen ratio in the air mixture and so hinder combustion.
An LP-EGR (low pressure EGR) system is one of the exhaust gas recirculation (EGR) systems. The LP-EGR system recirculates the exhaust gas passing through the turbine of the turbocharger to an intake path of an upstream side of the compressor.
However, the exhaust gas recirculated by the EGR system has high temperature and humidity. Therefore, condensed water is generated in an intake manifold when high temperature and humidity recirculated exhaust gas and the external air having a low temperature are mixed. The condensate water has very high acidity by various material included in exhaust gas.
If the condensate water flows into a cylinder of an engine, combustion of the engine becomes unstable. And various parts (i.e., compressor wheel, or compressor housing, and so on) are corroded by the condensate water having high acidity.
Further, a manifold absolute pressure sensor (MAP sensor) for measuring pressure of external air flowing into the intake manifold is mounted in the intake manifold, condensed water is frozen in surface of the manifold pressure sensor when temperature of external air is very low such cold weather.
As such, when the condensed water is frozen in the surface of the manifold pressure sensor, a pressure aperture for measuring pressure of external air formed in the manifold pressure sensor is blocked, thereby accuracy of pressure measured by the MAP sensor is deteriorated or there is a case that pressure of external air cannot be measured.
Further, when the parts (i.e., compressor wheel, or compressor housing, and so on) is frozen by freezing of condensed water, temperature of external air measured by the MAP sensor is distorted.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.